In recent years, a considerable amount of optical fiber has been added to the national communications infrastructure. While optical fiber provides a great deal more bandwidth than a comparable conventional wire cable, continuing increases in the available bandwidth are necessary. This is driven in part by the exponential growth in IP traffic.
In response to the increased demand for bandwidth, communications carriers and equipment vendors are researching means for simplifying the national communications infrastructure. One of the areas of research relates to means for bringing the IP and SONET/SDH transport layers closer to the common optical transport layer. Solutions in this area are anticipated to be very cost-effective.
Conventionally, network nodes use complex protocol stacks to provide an interface between IP, SONET/SDH etc., and the optical transport layer. The various protocol layers may repeatedly (and unnecessarily) perform very similar interface functions. Further, each of the protocol layers may have its own service provisioning, configuration management, billing and other operation services.
Currently available switching products are usually based on a common electrical switching fabric. The discontinuity of the optical layer within the switching layer creates several fundamental problems with respect to simplification of the communications interface. One of these problems is the scalability of these systems. Although the bandwidth and speed of these systems continues to increase, they are not expected to be able to meet the traffic demands of massive, content-based services. Even if these demands could be met, it is anticipated that the many interconnects and fabric elements required in a terabit electrical switching fabric would present an operational nightmare in terms of the provisioning and management of the system.
Another of problems with the systems is that, while electrical switches may be fast, they are an order of magnitude slower than the photonic switches. Electrical chips can currently handle a data rate of about 2.5 Gbps, while a photonic switching element can switch a 40-nm bandwidth channel at nano second speed. Thus, the throughput of an electrical switching fabric will be substantially lower than a comparable photonic switching fabric.
A related problem is that, even though photonic switches have the potential to operate at much higher data rates than electrical switches, it is very difficult to implement a photonic switch at these data rates. As a result of these difficulties, photonic switching systems in the prior art do not switch data at the packet level. Instead, connections are maintained from a particular set of ingress edges to a particular set of egress edges. These connections remain in place for long periods of time (e.g., hours or even days). The time required to change the connections and the amount of data lost during the change is therefore insignificant in terms of the efficiency of the system. In other words, the ratio of the number of bits lost to the number of bits successfully transmitted is very low.